1. Field of the Invention
The invention relates to switching voltage regulators and to detection of fault conditions associated therewith.
2. Description of the Related Art
Switching voltage regulators are used in power supplies to provide, e.g., regulated DC output voltage from an unregulated AC input. Typical consumer products involving such switching regulators include cell phone chargers, laptop or printer power supplies (so-called “bricks”), and embedded PC power supplies. One aspect of such switching regulators is that abnormal conditions in the switching regulator can arise that cause safety concerns. For example, abnormal conditions such as short circuits can lead to risk of electric shock or overheating.
In order to address safety concerns, various safety specifications such as IEC 60950-1 provide guidance related to current, voltage and power for electronics equipment. One of the safety requirements specified by IEC 60950-1 is Limited Power Source (LPS), which specifies that the maximum output power delivery should be limited to a level that is dependent on the rated output voltage. For example, a DC power source that has a 32 Volt output voltage should not deliver more than 100VA for more than 60 seconds. The table below shows limits for inherently limited power sources where UCC is output voltage, Isc is maximum output current and S (VA) is maximum output VA measured 60 seconds after application of the load according to IEC 60950-1.
Output voltageOutput currentApparent Power(Ucc)(Isc)(S)V a.c.V d.c.AVA≦20≦20≦8≦5 × Ucc20 < Ucc ≦ 3020 < Ucc ≦ 30≦8≦100—30 < Ucc ≦ 60≦150/Ucc≦100
In order to meet LPS requirements, one approach is to provide cycle-by-cycle monitoring of maximum output delivery. However, cycle-by-cycle monitoring to meet LPS requirements can result in increased cost and may be difficult to implement in certain systems.